1. Field of the Invention
This invention relates to a self temperature control type glow plug which is used in a diesel engine to cope with cold starting.
2. Description of Prior Art
In a glow plug for use in a diesel engine, the energized glow plug burns a part of vaporized fuel injected into an auxiliary combustion chamber of the diesel engine cylinder to cope with cold starting.
Since this type of the glow plug needs a rapid temperature-rise characteristic, and having a recent tendency to be kept energized longer after starting the engine, it has been suggested to employ a ceramic heater which has a glow resistor embedded therein. It, however, has a possibility that the resistor may be melt down due to a rapid heating while the ceramic resistor may be broken due to thermal shock when the glow resistor is rapidly energized since the glow resistor is generally provided with high electrical resistance value.
In order to prevent the breakage and melt-down, a temperature-regulating resistor is connected in series with the glow resistor so as to provide a self-regulating type glow plug as shown in Japanese Patent Publication No. 55369/89 in which the temperature-regulating resistor works to adjust an amount of electrical current flowing through the glow resistor.
The self-regulating glow plug shown in Japanese Patent Publication No. 55369/89, however, has disadvantages that the self-regulation function may be significantly reduced to shorten an operating period of its service life depending upon an electrical resistance ratio of the temperature-regulating resistor to the glow resistor.
Therefore, it is an object of the invention to obviate the above disadvantages, and providing a self-regulating type glow plug which is capable of enhancing its self-regulating function to ensure an extended period of service life with a relatively simple construction.